How do I copy and paste nodes?
You can copy nodes with Ctrl+c and paste them with Ctrl+v in the Node Editor. This will work with one material or multiple materials,lamp node trees as well as compositing nodes and World node tree. You cannot copy and paste compositing nodes into material node trees and material nodes into compositing node trees, but it seems you can copy/paste between material,light and World node trees. 

If you need multiple objects to have the same material, you can select them all with the one with the desired material being the last selected(active) and hit Ctrl+l -> Materials. They will then have the same material that will change on all of the objects if edited. If you want to edit the material of an object separately, you need to make it unique(single user) by clicking this number icon identifying how many users the material has:



or you could select multiple objects in the 3d viewport, hit u and choose "Material+Tex".